1. Field of the Invention
The present invention relates to a recording tape cartridge accommodating, within a case, a single reel on which is wound a recording tape, such as a magnetic tape or the like, which is used as a recording/playback medium mainly of computers or the like.
2. Description of the Related Art
Conventionally, recording tape cartridges (magnetic tape cartridges) have been known in which a magnetic tape, which is used as a data recording/playback medium of a computer or the like, is wound on a single reel, and the reel is accommodated in a case formed of synthetic resin. In such a recording tape cartridge, as shown in FIG. 8, at a reel 160, a reel hub 162 and a lower flange portion 164 are molded integrally of a synthetic resin. The reel hub 162 is cylindrical, and a magnetic tape T is wound therearound. The lower flange portion 164 juts out in the radial direction from the outer periphery of the bottom end of the reel hub 162. Further, an upper flange portion 166, which has the same configuration as the lower flange portion 164, is joined to the top end of the reel hub 162 by ultrasonic welding or the like.
The lower flange portion 164 side of the reel hub 162 is closed by a floor wall 168 in whose center a through hole 168A is formed. A reel gear 170, which is for driving and rotating the reel 160, is carved in an annular form at the outer peripheral portion of the bottom surface of the floor wall 168. A reel plate 172, which is an annular metal plate in which is formed a through hole 172A which is slightly smaller than the through hole 168A, is mounted by insert molding or the like to the inner side of the reel gear 170.
A circular gear opening 156 is formed in the center of the bottom surface of a lower case 154. The reel gear 170, which is provided in an annular form at the bottom surface of the reel 160, the reel plate 172, and the like, are exposed from the gear opening 156. Accordingly, the reel plate 172 of a recording tape cartridge 150 is attracted by a magnet (not illustrated) provided at a rotating shaft 200 of a drive device, and the reel gear 170 meshes with a driving gear 202 provided at the rotating shaft 200, and the reel 160 is driven to rotate.
An engaging gear 176 is carved in an annular form at the outer peripheral portion of the top surface of the floor wall 168 which faces the inner side of the reel hub 162. The engaging gear 176 meshes with a braking gear 186 of a braking member 180 which is inserted in the reel hub 162. The braking member 180 is provided so as to prevent rotation of the reel 160 when the recording tape cartridge 150 is not being used (e.g., is not loaded in a drive device or the like). The braking member 180 is formed in the shape of a disc at which the braking gear 186 is carved in an annular form at the outer peripheral portion of the bottom surface of the braking member 180.
A columnar projecting portion 184 which is substantially U-shaped in plan view (and which will hereinafter be called the U-shaped projecting portion 184) stands erect at the top surface of the braking member 180 so as to oppose the open side. The rotation of the braking member 180 is impeded due to two retention pins 194, which project so as to be lined up next to one another at the center of the inner surface of an upper case 152, being inserted in at the inner surface of the U-shaped projecting portion 184. An annular projection 192 projects at the substantial center of the inner surface of the upper case 152 and at the outer side of the retention pins 194. An annular groove 182 is provided at the top surface of the braking member 180 at the outer side of the U-shaped projecting portion 184. One end of a coil spring 190 is fit-in at the inner side of the annular projection 192, whereas the other end of the coil spring 190 is fit-in in the annular groove 182, such that the coil spring 190 is held between the upper case 152 and the braking member 180.
Accordingly, due to the braking member 180 being urged downward by the coil spring 190 and the braking gear 186 engaging with the engaging gear 176, the reel 160 does not rotate inadvertently when the recording tape cartridge 150 is not being used. Further, a substantially columnar projection 188 is inserted into the through hole 168A so as to have play therewith and to project at the center of the bottom surface of the braking member 180. When the recording tape cartridge 150 is being used, the braking member 180 is pushed upward via the projection 188 against the urging force of the coil spring 190 by an engaging member 204 provided at the center of the rotating shaft 200 of the drive device. The braking gear 186 moves apart from the engaging gear 176, and the meshing of the two is cancelled. In this way, the reel 160 becomes able to rotate. (See, for example, Japanese Patent Application Laid-Open (JP-A) No. 63-251983.)
In the recording tape cartridge 150 having a structure such as that described above, the reel gear 170 is exposed from the gear opening 156 which is formed in the bottom surface of the lower case 154. Therefore, when the recording tape cartridge 150 is not being used, it is easy for dust and the like to enter in from the gear opening 156. For example, as shown in FIG. 8, conventionally, dustproofing measures have been taken by providing an annular groove 174 at the outer side of the reel gear 170, and by fitting a rib 158, which stands erect at the peripheral portion of the gear opening 156, into this annular groove 174.
However, even with this structure, the dustproofing measures are not sufficient enough with respect to dust which enters in from the through holes 168A, 172A. Namely, because the projection 188 of the braking member 180 must be inserted into the through hole 168A so as to have play, a gap is formed between the projection 188 and the through hole 168A. There is the concern that dust or the like (shown by the arrow) will penetrate in by passing through between the braking gear 186 and the engaging gear 176, and will adhere to the magnetic tape T. Therefore, conventionally, an improvement in the dustproof quality at this portion has been desired.